Papers by Keyword: Leaching

Abstract: In order to make the natural quartz up to the standard of high purity quartz sands, quartz ores are processed to obtain high purity quartz sands by the purifying technologies which include grinding, high-intensity magnetic concentration, flotation and acid leaching, washed by deionized water. The phase, morphology and composition of the prepared quzrtz sands were determined by X-ray diffraction, scanning electron microscope and inductively coupled plasma spectrometers.The results show that impurity minerals adsorb onto the quartz mineral surfaces. Magnetic minerals were removed by magnetic concentration experiment, while other impurities were removed by flotation and acid leaching experiments and they show excellent cleaning effect. Finally a high purity quartz product which contains higher than 99.95% SiO₂, less than 0.003% Fe₂O₃, and less than 0.01% Al₂O₃ was obtained.

Abstract: Heating iron ore fine particles using microwave energy has been effective due to the different interactions between minerals and gangue in the magnetic field generated by the microwave. In this way, this paper proposes to use microwave energy to heat the particles of iron ore to promote micro cracks and fissures, which would facilitate the comminution and pulverization process to produce pellet feed. It was analyzed different conditions of heating and cooling in the comminution step. By using techniques of scanning electron microscopy (SEM) and image analysis it was possible to assess and quantify the micro cracks and subsequent analysis of the energy and size fragmentation in the comminution step of ultrafine particles.

Abstract: This study addresses the recovery of recovery of zinc (Zn) and manganese (Mn) from spent dry cell (Zn-C battery) batteries using a hydrometallurgical approach. Every year, a significant number of Zn-C dry cell batteries are consumed and disposed worldwide. Zn-C dry cell batteries constitute more than 60% of Zn and Mn together. Higher amount of Zn and Mn present in Zn-C dry cells shows an industrial interest in recycling and recovering Zn and Mn. In this study the recovery of Zn and Mn from spent dry cells was investigated through an energy efficient hydrometallurgical route. Zn-C batteries were manually dismantled to collect the battery paste. Neutral leaching was carried out to remove potassium and non-metal contents. The battery powder was leached in sulfuric acid medium with glucose as reducing agent. The experiments were conducted according to ‘24 full factorial design’. The purpose of the design was to identify the most effective and optimum condition for Zn and Mn recovery from spent Zn-C batteries. Using the optimum operating condition, up to 86.54 % of Mn and 82.19% of Zn were recovered from the original battery powder.

Abstract: Orthodontic elastic bands made from natural rubber continue to be commonly used due to their favorable characteristics. However, there are concerns associated cytotoxicity due to harmful components released during conventional vulcanization (sulfur-based method). With the co-operation of The National Metal and Materials Technology Center (MTEC) and Faculty of Dentistry Mahidol University, a new method was introduced to reduce toxic components by leaching the orthodontic elastic bands with NaOH solution. The objective of this study was to evaluate the mechanical properties of Thai and commercial orthodontic elastic brands (Ormco and W&H) leached with NaOH solution. Three elastic brands (N =30, size 1⁄4 inch ,4.5 oz.) were tested for mechanical properties in terms of initial extension force, residual force, force loss, breaking strength and maximum displacement using a Universal Testing Machine. The results showed that force loss significantly decreased in Thai-LEACH and W&H-LEACH, whereas the values increased in Ormco-LEACH (P<0.05). The data exhibited a significantly decrease in breaking strength with Thai-LEACH and Ormco-LEACH, whereas all 3 brands revealed a significantly decrease in maximum displacement with the leaching process (P<0.05). In conclusion, leaching with NaOH solution is a new method, which can remove toxic components from orthodontic latex elastic bands. However, this process can affect their mechanical properties. Leached elastic bands from Thai had comparable properties with Ormco and have potential to be developed as a promising product.

Abstract: Because of its environmental and economic benefits, part of cement is replaced by limestone fillers (LS). However, the effect of LS on the chemical degradation of cement-based materials is still unclear. In this study, accelerated leaching and carbonation were applied on cement pastes to study the effects of LS replacement on the degradation rates and microstructural alterations of degraded materials. Ammonium nitrate solution was used to accelerate the leaching process, while carbonation was speeded up by applying an elevated pressure gradient of pure CO₂ on samples with 65% relative humidity. The carbonation rate was characterized by phenolphthalein carbonation depth and CO₂ uptake, while leaching rate was quantified by phenolphthalein leaching depth and Ca-leached amount. Leached/carbonated samples were analyzed by a series of post-analysis techniques to characterize the microstructural and mineralogical changes. Results showed that, for a similar w/c ratio, a higher LS replacement resulted in lower leaching rate. For carbonation, LS replacement promoted the CO₂ uptake despite similar carbonation depth. Furthermore, LS replacement led to less C-S-H carbonation compared to samples without LS.

Abstract: Experimental results for nanosecond electromagnetic impulses (NEMI) impact on precious metals leaching process from sulphidic ores are presented. A possibility of an intensification of leaching process of Au, Ag, Cu is established. The extraction of silver increases by 70 %, gold – by 40 %. The samples of sulphidic ores from the pit of JSC NPF "Bashkir gold mining company" are taken as objects of research. The use of economic electronic generators is suggested herein. They create impulses of 1 nanosecond, the front of 0.1 nanoseconds, amplitude of 6-15 kV impulses, 1 kHz frequency of repetition, consumed power from an electric network is less than 100 W. Energy in one impulse is 10^–3 J. The pulse field changes the valence of metals of impurity towards decrease. It changes the current of chemical reactions in a mineral matrix. The local heating of the precious metals interspersed particles and destruction of a mineral matrix are also possible.

Abstract: Pyrite, mineral largely found in nature, is considered a solid waste when is obtained from the coal mining. However, can be precursor of products like: sulphur, sulphuric acid, hematite, sulphur dioxide, fertilizers and iron sulfates. Several studies also point it property of semiconduction and it use in solar cells. Increase it purity level is important for transforming it in products with more aggregate value. Thus, the present work suggests a purification route for the reduction in soluble salts in water, organics and quartz associated with pyrite from the coal mining beneficiation. The used methods were solubilization in hot water and in organic solvent (dichloromethane). Were applied XRD, FTIR, total sulphur determination, and gas helium picnometry. Comparing the results obtained for the “in nature” pyrite with the purified one, proved the efficiency of the proposed method.

Abstract: The diversity of industrial solid waste has grown exponentially in recent years, requiring waste management strategies focused on the reduction of associated environmental impacts. The solidification/stabilization (S/S) technique is increasingly used in the disposal or recycling of this waste. The Brazilian standard about the leaching of hazardous compounds in waste is being used to evaluate S/S products in their end disposal in landfills, with no description of any protocol to investigate performance during their life cycle, as observed when they are used as admixture to building materials. In this context, this study describes a qualitative review of leaching methods in use to assess S/S products in Brazil, in comparison with the main techniques adopted in other countries.

Abstract: The pyrometallurgical method of tin extraction from lead free solder dross after leaching treatment is discussed. The solder dross is sieved into 75 μm was used for the experiment. The samples were leached using 0.3 M HCl, 12 hours stirring times and temperature of 60°C was used for the leaching before thermal treatment. The sample was thermally treated at temperature of 650,850 and 1050°C. The increase of heating temperature causes the lowering of the tin extraction. The optimum parameter for heating temperature is 850°C with 98.71% of tin recovery.

Abstract: Based on the results of previous research it could be stated that the deterioration of concrete elements by leaching process could be described by the simplified diffusion function. However the results of Schneider and Chen showed that the deterioration of concrete elements by leaching could differ significantly if they are subjected to permanent bending performance. Their experimental data pointed out that after a certain time the deterioration course of loaded concrete elements significantly changes and these elements lose their strength faster than the unloaded control specimens.Article outlines the possible theoretical solution of this phenomenon. The developed theoretical models where applied to the experimental results of Schneider and Chen [3], [2]. The main task was to find a simplified engineering solution to the problem of the stress corrosion of the concrete in ammonium nitrate solution.